Polyaxial bone screw with shank-retainer insert capture

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application is a continuation of U.S. patent application Ser. No. 12/154,460, filed May 23, 2008, now U.S. Pat. No. 8,257,396, which claimed the benefit of U.S. Provisional Application No. 60/931,362 filed May 23, 2007, and incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 10/818,555 filed Apr. 5, 2004, now U.S. Pat. No. 8,052,724, that is a continuation of U.S. patent application Ser. No. 10/464,633 filed Jun. 18, 2003, now U.S. Pat. No. 6,716,214 and a continuation-in-part of U.S. patent application Ser. No. 10/651,003, filed Aug. 28, 2003, now U.S. Pat. No. 8,137,386, all of which are incorporated by reference herein. This application is also a continuation-in-part of U.S. patent application Ser. No. 11/140,343 filed May 27, 2005, now U.S. Pat. No. 7,776,067, also incorporated by reference herein.

BACKGROUND OF THE INVENTION

0002The present invention is directed to polyaxial bone screws for use in bone surgery, particularly spinal surgery, and particularly to capture structures and inserts for such screws.

0003Bone screws are utilized in many types of spinal surgery in order to secure various implants to vertebrae along the spinal column for the purpose of stabilizing and/or adjusting spinal alignment. Although both closed-ended and open-ended bone screws are known, open-ended screws are particularly well suited for connections to rods and connector arms, because such rods or arms do not need to be passed through a closed bore, but rather can be laid or urged into an open channel within a receiver or head of such a screw.

0004Typical open-ended bone screws include a threaded shank with a pair of parallel projecting branches or arms which form a yoke with a U-shaped slot or channel to receive a rod. Hooks and other types of connectors, as are used in spinal fixation techniques, may also include open ends for receiving rods or portions of other structure.

0005A common mechanism for providing vertebral support is to implant bone screws into certain bones which then in turn support a longitudinal structure such as a rod, or are supported by such a rod. Bone screws of this type may have a fixed head or receiver relative to a shank thereof. In the fixed bone screws, the rod receiver head cannot be moved relative to the shank and the rod must be favorably positioned in order for it to be placed within the receiver head. This is sometimes very difficult or impossible to do. Therefore, polyaxial bone screws are commonly preferred.

0006Open-ended polyaxial bone screws allow rotation of the head or receiver about the shank until a desired rotational position of the head is achieved relative to the shank. Thereafter, a rod can be inserted into the head or receiver and eventually the receiver is locked or fixed in a particular position relative to the shank.

0007During the rod implantation process it is desirable to utilize bone screws or other bone anchors that have components that remain within the bone screw and further remain properly aligned during what is sometimes a very lengthy, difficult procedure. For example, some bone screws desirably include compression inserts or other parts that are designed to securely and fully engage surface portions of a rod or other longitudinal connecting member.

SUMMARY OF THE INVENTION

0008A polyaxial bone screw assembly of the present invention includes a shank having a generally elongate body with an upper end portion a neck below the upper end portion and a lower threaded portion for fixation to a bone. The upper end portion includes at least first and second surfaces, the second surface being at least partially inset or at least a portion thereof spaced inwardly from the first surface. For example, the first and second surfaces may be in the form of two substantially cylindrical surface portions of different widths or diameters or a cylindrical surface portion and a conical surface portion that is inset from the cylindrical surface portion. Alternatively, the upper end portion may include a laterally extending alignment structure in the form of a fin, rib or lug that can at least partially fill a gap or slot in a retainer component and block rotation between these two parts.

0009The bone screw assembly further includes a lockable receiver coupling member having a top portion and a base. The top portion is open and has a channel. The base includes an inner surface partially defining a cavity and a lower aperture or opening to an exterior of the base. The channel of the top portion communicates with the cavity, which in turn communicates with the base lower opening; such opening is sized and shaped to receive the shank upper end portion into the receiver cavity. The parts are arranged such that the shank neck is in close alignment with and positioned directly below the receiver cavity.

0010The bone screw assembly also includes an open ring-like retainer structure defining a gap or slit and further having a discontinuous internal surface sized and shaped to be expandedly and compressedly received over the lower conical or cylindrical surface portion to capture, house and hold the retainer and shank upper end portion within the lockable receiver coupling member. In the illustrated embodiment, the fin of the shank upper portion is disposed within the gap or slit of the retainer structure. The external surface of the retainer structure is configured to be in slidable, pivotable engagement with a seating surface defining a portion of the cavity of the receiver. Preferably, the retainer structure external surface and the mating receiver inner seating surface are substantially spherical. However, it is noted that the mating surfaces may be of another shape, such as conical, non-conical, cylindrical, or tapered, especially for the receiver cavity inner seating surface. The cooperating shapes of the retainer external surface and the receiver seating surface enable selective angular positioning of the shank body with respect to the receiver.

0011The illustrated bone screw assembly further includes a compression or pressure insert disposed between the shank upper portion and a longitudinal connecting member, such as a rod, being held in place by the bone screw. An upper or top surface of the shank upper end portion is sized and shaped for frictionally engagement with a lower surface of the pressure insert. In one embodiment according to the invention, the shank upper end portion is convex, and the lower surface of the pressure insert is concave. In one embodiment according to the invention, the shank upper portion includes a non-slip tool engagement formation with an internal drive. The shank upper top surface can include knurling and the shank upper portion is sized in axial length such that the shank upper surface engages the compression insert at a location substantially spaced from the retainer structure. Thus, at any operational pivoted position of the bone screw shank with respect to the receiver, the compression insert is always spaced from the retainer structure and never engages the same, advantageously providing for the exertion of pressure exclusively onto the stronger integral shank upper portion. The retainer structure of the present invention is split and thus could become twisted or mis-aligned if placed under the opposing shear forces and even torsional forces caused if the pressure insert were allowed to press upon an edge or surface of the retainer structure when it is in a pivoted, angled or oblique position. In the embodiments of the present invention, the shank upper end portion includes an axially directed length adequate to prevent such undesirable engagement between the pressure insert and the retainer structure. The retainer structure is advantageously disposed substantially below the pressure insert and between the shank upper portion and the receiver seating surface, with only the shank upper portion pressing the retainer structure against the receiver seating surface. The fact that the retainer structure can only engage the shank upper end portion and the receiver, and never the pressure insert, and still move in a polyaxial way with respect to the receiver is a unique and novel feature for the invention.

OBJECTS AND ADVANTAGES OF THE INVENTION

0012Therefore, objects of the invention include: providing a polyaxial bone screw having a shank with off-set surfaces that cooperate with a retaining structure that is configured with inset capture surfaces for retaining an upper portion of the shank in a lockable bone screw receiver coupling member and also configured for polyaxial motion with respect to the receiver prior to locking; providing such a polyaxial bone screw that includes a pressure insert that exerts pressure exclusively on the integral and stronger shank upper end portion and that is substantially spaced from the retaining structure; providing a lightweight, low profile polyaxial bone screw that assembles in such a manner that the components cooperate to create an overall structure that prevents unintentional disassembly; providing a polyaxial bone screw with features that provide adequate frictional or gripping surfaces for bone implantation tools and may be readily, securely fastened to each other and to bone; and providing apparatus and methods that are easy to use and especially adapted for the intended use thereof and wherein the apparatus are comparatively inexpensive to make and suitable for use.

0013Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.

0014The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

0015<figref idref="DRAWINGS">FIG. 1</figref> is an exploded perspective view of a polyaxial bone screw assembly according to the present invention having a shank, a receiver, a retainer and a compression insert and further shown with a closure structure.

0016<figref idref="DRAWINGS">FIG. 2</figref> is an enlarged front elevational view of the shank of <figref idref="DRAWINGS">FIG. 1</figref>.

0017<figref idref="DRAWINGS">FIG. 3</figref> is an enlarged perspective view of the retainer of <figref idref="DRAWINGS">FIG. 1</figref>.

0018<figref idref="DRAWINGS">FIG. 4</figref> is an enlarged cross-sectional view taken along the line <b>4</b>-<b>4</b> of <figref idref="DRAWINGS">FIG. 3</figref>.

0019<figref idref="DRAWINGS">FIG. 5</figref> is an enlarged and partial exploded front elevational view of the shank, retainer and receiver of <figref idref="DRAWINGS">FIG. 1</figref> with portions broken away to show the detail thereof showing the shank and retainer in a first stage of assembly.

0020<figref idref="DRAWINGS">FIG. 6</figref> is an enlarged and partial front elevational view similar to <figref idref="DRAWINGS">FIG. 5</figref> showing the shank being uploaded into the retainer in a subsequent stage of assembly.

0021<figref idref="DRAWINGS">FIG. 7</figref> is an enlarged and partial front elevational view similar to <figref idref="DRAWINGS">FIG. 6</figref> showing a subsequent stage of assembly.

0022<figref idref="DRAWINGS">FIG. 8</figref> is an enlarged and partial front elevational view similar to <figref idref="DRAWINGS">FIG. 7</figref> and also including the compression insert, showing a subsequent stage of assembly.

0023<figref idref="DRAWINGS">FIG. 9</figref> is an enlarged side elevational view of the compression insert of <figref idref="DRAWINGS">FIG. 1</figref> with portions broken away to show the detail thereof.

0024<figref idref="DRAWINGS">FIG. 10</figref> is an enlarged perspective view of the assembly of <figref idref="DRAWINGS">FIG. 1</figref> shown assembled with a rod and with portions broken away to show the detail thereof.

0025<figref idref="DRAWINGS">FIG. 11</figref> is an exploded perspective view of a second embodiment of a polyaxial bone screw assembly according to the present invention having a shank, a receiver, a retainer and a compression insert and further shown with a closure structure.

0026<figref idref="DRAWINGS">FIG. 12</figref> is an enlarged perspective view of the retainer of <figref idref="DRAWINGS">FIG. 11</figref>.

0027<figref idref="DRAWINGS">FIG. 13</figref> is an enlarged cross-sectional view taken along the line <b>13</b>-<b>13</b> of <figref idref="DRAWINGS">FIG. 12</figref>.

0028<figref idref="DRAWINGS">FIG. 14</figref> is an enlarged perspective view of the assembly of <figref idref="DRAWINGS">FIG. 11</figref> shown assembled with a rod and with portions broken away to show the detail thereof.

DETAILED DESCRIPTION OF THE INVENTION

0029As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. It is also noted that any reference to the words top, bottom, up and down, and the like, in this application refers to the alignment shown in the various drawings, as well as the normal connotations applied to such devices, and is not intended to restrict positioning of bone attachment assemblies of the application and cooperating connecting members in actual use.

0030With reference to <figref idref="DRAWINGS">FIGS. 1-10</figref>, the reference number <b>1</b> generally represents an embodiment of a polyaxial bone screw apparatus or assembly according to the present invention. The assembly <b>1</b> includes a shank <b>4</b> that further includes a threaded body <b>6</b> integral with an upper portion <b>8</b>; a receiver <b>10</b>; an open retainer structure or ring <b>12</b>; and a compression insert <b>14</b>. The shank <b>4</b>, receiver <b>10</b>, retainer structure <b>12</b>, and compression insert <b>14</b> preferably are factory assembled prior to implantation of the shank body <b>6</b> into a vertebra (not shown).

0031With further reference to <figref idref="DRAWINGS">FIG. 1</figref>, also shown is a closure structure <b>18</b> for biasing a longitudinal connecting member such as a rod <b>21</b> having a cylindrical surface <b>22</b> against the compression insert <b>14</b> that in turn presses upon the shank upper portion <b>8</b> which biases the retainer <b>12</b> into fixed frictional contact with the receiver <b>10</b>, so as to fix the rod <b>21</b> relative to the vertebra (not shown). The receiver <b>10</b> and the shank <b>4</b> cooperate in such a manner that the receiver <b>10</b> and the shank <b>4</b> can be secured at any of a plurality of angles, articulations or pivotal alignments relative to one another and within a selected range of angles both from side to side and from front to rear, to enable flexible or articulated engagement of the receiver <b>10</b> with the shank <b>4</b> until both are locked or fixed relative to each other near the end of an implantation procedure.

0032The shank <b>4</b>, best illustrated in <figref idref="DRAWINGS">FIGS. 1</figref>, <b>2</b> and <b>5</b>, is elongate, with the shank body <b>6</b> having a helically wound bone implantable thread <b>24</b> extending from near a neck <b>26</b> located adjacent to the upper portion <b>8</b> to a tip <b>28</b> of the body <b>6</b> and extending radially outwardly therefrom. During use, the body <b>6</b> utilizing the thread <b>24</b> for gripping and advancement is implanted into the vertebra (not shown) leading with the tip <b>28</b> and driven down into the vertebra with an installation or driving tool, so as to be implanted in the vertebra to near the neck <b>26</b>, and as is described more fully in the paragraphs below. The shank <b>4</b> has an elongate axis of rotation generally identified by the reference letter A.

0033The neck <b>26</b> extends axially upwardly from the shank body <b>6</b>. The neck <b>26</b> may be of reduced radius as compared to an adjacent top <b>32</b> of the threaded body <b>6</b>. Further extending axially upwardly from the neck <b>26</b> is the shank upper portion <b>8</b> that provides a connective or capture apparatus disposed at a distance from the threaded body top <b>32</b> and thus at a distance from the vertebra when the body <b>6</b> is implanted in the vertebra.

0034The shank upper portion <b>8</b> is configured for a polyaxial connection between the shank <b>4</b> and the receiver <b>10</b> and capturing the shank <b>4</b> upper portion <b>8</b> in the receiver <b>10</b>. The illustrated upper portion <b>8</b> generally includes an outer conical surface portion <b>33</b> located adjacent the neck <b>26</b>; an annular planar retainer seat portion <b>34</b>; a substantially cylindrical surface portion <b>35</b>; a curved and annular upper surface <b>36</b> and a planar top surface <b>38</b>. The planar top surface <b>38</b> is substantially perpendicular to the cylindrical surface portion <b>35</b> and substantially parallel to the seat portion <b>34</b>. As shown in the drawings and described more fully below, the height of the portion <b>35</b> along the axis A ensures that the cooperating lower pressure insert <b>14</b> is separated from and never engages the retainer <b>12</b> throughout a full range of polyaxial motion of the assembly <b>1</b> in all directions. The conical portion <b>33</b> extends between the neck <b>26</b> and the retainer seat <b>34</b>. The retainer seat <b>34</b> defines a lower edge <b>39</b> of the cylindrical portion <b>35</b>. A structure in the form of a rib or fin <b>40</b> extends laterally from the conical portion <b>33</b> and a lower part of the cylindrical portion <b>35</b>. A tool engagement internal drive feature or structure <b>42</b> is formed in the top end surface <b>38</b> for non-slip engagement with a driving tool. A driving tool (not shown) has a driving projection configured to fit within the tool engagement structure <b>42</b> for both driving and rotating the shank body <b>6</b> into the vertebra.

0035The upper surface <b>36</b> of the shank <b>4</b> is preferably curved or radiused as shown in the drawings, for contact engagement or positive mating engagement with the compression insert <b>14</b>, when the bone screw assembly <b>1</b> is assembled, as shown in <figref idref="DRAWINGS">FIG. 10</figref> and in any pivotal alignment of the shank <b>4</b> relative to the receiver <b>10</b>. The illustrated surface <b>36</b> also has approximately the same radius as an inner spherical seating surface of the receiver <b>10</b>, allowing for clearance of the shank <b>4</b> with respect to the receiver <b>10</b> and thus a desired degree and magnitude of articulation of the shank <b>4</b> with respect to the receiver <b>10</b>, as will be described in greater detail below. In certain embodiments, the surface <b>36</b> is smooth. While not required in accordance with the practice of the invention, the surface <b>36</b> may be scored or knurled to further increase frictional positive mating engagement between the surface <b>36</b> and the compression insert <b>14</b>.

0036The shank <b>4</b> shown in the drawings is cannulated, having a small central bore <b>44</b> extending an entire length of the shank <b>4</b> along the axis A. The bore <b>44</b> is defined by an inner cylindrical wall of the shank <b>4</b> and has a circular opening <b>46</b> at the shank tip <b>28</b> and an upper opening communicating with the internal drive <b>42</b>. The bore <b>44</b> is coaxial with the threaded body <b>6</b> and the upper portion <b>8</b>. The bore <b>44</b> provides a passage through the shank <b>4</b> interior for a length of wire (not shown) inserted into the vertebra (not shown) prior to the insertion of the shank body <b>6</b>, the wire providing a guide for insertion of the shank body <b>6</b> into the vertebra (not shown).

0037With reference to <figref idref="DRAWINGS">FIGS. 2 and 5</figref>, the retainer seat <b>34</b> of the shank upper portion <b>8</b> is formed by the off-set positioning and cooperation of the surface portions <b>33</b> and <b>35</b>. The off-set nature of the surface portion <b>35</b> with respect to the surface portion <b>33</b> creates the surface <b>34</b> that is substantially planar, annular and disposed perpendicular to the axis A of the shank and sized and shaped to engage the retainer structure <b>12</b>, as will be described in greater detail below. The illustrated conical surface portion <b>33</b> is primarily sized and shaped for full frictional engagement with the retainer structure <b>12</b>. The illustrated cylindrical surface portion <b>35</b> is sized and shaped to have a portion thereof being in frictional engagement with a portion of the retainer structure <b>12</b>. Furthermore, the surface portion <b>34</b> is sized and shaped to provide a space between the structure <b>12</b> and the compression insert <b>14</b>. Specifically, the cylindrical surface portion <b>35</b> has an axial length (with respect to the axis A) that is sufficient to keep an engaged retainer structure <b>12</b> in spaced apart relation with an engaged insert <b>14</b> in any and all angles, articulations or pivotal alignments of the shank <b>4</b> with respect to the receiver <b>10</b>. Thus, at no time during assembly or operation does the insert <b>14</b> directly engage the retainer structure <b>12</b> (see <figref idref="DRAWINGS">FIG. 10</figref>, for example).

0038The rib or fin <b>40</b> that extends radially outwardly from both the conical portion <b>33</b> and a part of the cylindrical portion <b>35</b> includes a top surface <b>50</b>, a bottom surface <b>52</b>, a pair of opposed and substantially parallel side surfaces <b>54</b> and <b>55</b>, an outer curved surface <b>56</b> and a bevel <b>58</b> disposed between the top surface <b>50</b> and the outer curved surface <b>56</b>. In the illustrated embodiment, the bottom surface <b>52</b> is a narrow rim extending between the outer curved surface <b>56</b> and the conical surface portion <b>33</b> of the shank upper portion <b>8</b> that is disposed near the neck <b>26</b>. The top surface <b>50</b> is substantially planar, disposed substantially perpendicular to the axis A and extending from the cylindrical surface portion <b>35</b> at a location spaced from the curved upper surface <b>36</b>. The surfaces <b>56</b> and <b>58</b> are flush with outer surfaces of the retainer structure <b>12</b> when the seat <b>34</b> operatively engages the retainer <b>12</b> as will be discussed in greater detail below.

0039To provide a biologically active interface with the bone, the threaded shank body <b>6</b> may be coated, perforated, made porous or otherwise treated. The treatment may include, but is not limited to a plasma spray coating or other type of coating of a metal or, for example, a calcium phosphate; or a roughening, perforation or indentation in the shank surface, such as by sputtering, sand blasting or acid etching, that allows for bony ingrowth or ongrowth. Certain metal coatings act as a scaffold for bone ingrowth. Bio-ceramic calcium phosphate coatings include, but are not limited to: alpha-tri-calcium phosphate and beta-tri-calcium phosphate (Ca₃(PO₄)₂, tetra-calcium phosphate (Ca₄P₂O₉), amorphous calcium phosphate and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). Coating with hydroxyapatite, for example, is desirable as hydroxyapatite is chemically similar to bone with respect to mineral content and has been identified as being bioactive and thus not only supportive of bone ingrowth, but actively taking part in bone bonding. In association with such coating of the shank, the lockable receiver coupling member can be configured to rigidly lock onto a bored element or sleeve member that can slide on the rod or core longitudinal connecting member even after rigid locking together of the receiver and the shank, thereby allowing continued motion of the spine.

0040Referring to <figref idref="DRAWINGS">FIGS. 1 and 5</figref>, the receiver <b>10</b> has a generally U-shaped appearance with a partially cylindrical inner profile and a substantially curved or cylindrical outer profile; however, the outer profile could also be of another configuration, for example, faceted. The receiver has an axis of rotation B that is shown in <figref idref="DRAWINGS">FIG. 1</figref> as being aligned with and the same as the axis of rotation A of the shank <b>4</b>, such orientation being desirable during assembly of the receiver <b>10</b> with the shank <b>4</b>, the retainer structure <b>12</b> and the insert <b>14</b>. With reference to <figref idref="DRAWINGS">FIG. 10</figref>, after the receiver <b>10</b> is pivotally attached to the shank <b>4</b>, and the assembly <b>1</b> is implanted in a vertebra (not shown), the axis B is typically disposed at an angle with respect to the axis A of the shank <b>4</b>.

0041The receiver <b>10</b> includes a base <b>60</b> integral with a pair of opposed substantially similar or identical upstanding arms <b>62</b> forming a U-shaped cradle and defining a U-shaped channel <b>66</b> between the arms <b>62</b> with an upper opening <b>67</b> and a lower seat <b>68</b> having substantially the same radius as the rod <b>21</b> for operably receiving the rod <b>21</b>. Each of the arms <b>62</b> has an interior surface <b>70</b> that defines the inner cylindrical profile and includes a partial helically wound guide and advancement structure <b>72</b>. In the illustrated embodiment, the guide and advancement structure <b>72</b> is a partial helically wound interlocking flange form configured to mate under rotation with a similar structure on the closure structure <b>18</b>, as described more fully below. However, it is foreseen that the guide and advancement structure <b>72</b> could alternatively be a square thread, a buttress thread, a reverse angle thread or other thread like or non-thread like helically wound advancement structure for operably guiding under rotation and advancing the closure top downward between the arms <b>62</b>.

0042Tool engaging apertures <b>75</b> are formed on or through surfaces of the arms <b>62</b> that may be used for holding the receiver <b>10</b> during assembly with the shank <b>4</b> and the retainer structure <b>12</b> and also during the implantation of the shank body <b>6</b> into a vertebra (not shown). It is foreseen that tool receiving grooves or apertures may be configured in a variety of shapes and sizes and be disposed at other locations on the receiver arms <b>62</b>.

0043A pair of spring tabs <b>76</b>, each having an upper body portion <b>78</b> integral with a respective arm <b>62</b>, and a lower end <b>80</b> extending downwardly and inwardly from the respective upper body portion <b>78</b>. The tabs <b>76</b> are generally directed towards the axis B and downwardly away from the guide and advancement structure <b>72</b>. The lower ends <b>80</b> are thus positioned to engage the compression insert <b>14</b> and hold such insert in a desired position as will be described in greater detail below. The tabs <b>76</b> are typically initially disposed parallel to the axis B and then a tool (not shown) is inserted into the aperture <b>75</b> from outside of the receiver <b>10</b> to engage and push the respective tab <b>76</b>, thereby bending the tab <b>76</b> inwardly in a direction toward the axis B until the tab <b>76</b> is at a desired angular position, such as is illustrated in <figref idref="DRAWINGS">FIG. 5</figref>. Such bending of the tabs <b>76</b> may be performed either prior to or after assembly of the receiver <b>10</b> with the insert <b>14</b>, the shank <b>4</b> and the retainer <b>12</b>. In the illustrated embodiment, the tabs <b>76</b> are bent inwardly prior to installation with the components <b>14</b>, <b>4</b> and <b>12</b>. It is also foreseen that the tabs <b>76</b> may be machined or otherwise pre-fabricated to be angled or directed toward the axis B so as to engage the insert <b>14</b> as shown in the drawing figures. The illustrated tabs <b>76</b> are resilient, having a spring-like nature. Thus, when operatively cooperating with the insert <b>14</b>, the tabs <b>76</b> bias against the insert <b>14</b>, holding such insert in a desired position; and yet the tabs <b>76</b> are flexible enough to allow a user to make desired adjustments of the position of the insert <b>14</b> within the receiver <b>10</b>. The tabs could be replaced with crimp holes.

0044With further reference to <figref idref="DRAWINGS">FIG. 5</figref>, communicating with and located beneath the U-shaped channel <b>66</b> of the receiver <b>10</b> is a chamber or cavity, generally <b>82</b>, defined in part by an internal curvate or spherical seating surface <b>84</b> and an inner substantially cylindrical surface <b>86</b>. The cylindrical surface <b>86</b> that defines a portion of the cavity <b>82</b> opens upwardly into the U-shaped channel <b>66</b>. The inner surface <b>84</b> that is located below the surface <b>86</b> is sized and shaped for mating with the retainer structure <b>12</b>, as described more fully below.

0045The base <b>60</b> further includes a restrictive neck <b>88</b> defining a bore, generally <b>90</b>, communicating with the spherical surface <b>84</b> of the cavity <b>82</b> and also communicating with a lower exterior <b>92</b> of the base <b>60</b>. The bore <b>90</b> is coaxially aligned with respect to the rotational axis B of the receiver <b>10</b>. The neck <b>88</b> and associated bore <b>90</b> are sized and shaped to be smaller than an outer radial dimension of the retainer structure <b>12</b> when the structure <b>12</b> is attached to the shank upper portion <b>8</b>, so as to form a restriction at the location of the neck <b>88</b> relative to the retainer structure <b>12</b>, to prevent the retainer structure <b>12</b> and attached shank upper portion <b>8</b> from passing through the cavity <b>82</b> and out into the lower exterior <b>92</b> of the receiver <b>10</b>.

0046The retainer structure or open ring <b>12</b> is used to capture the shank upper portion <b>8</b> and retain the upper portion <b>8</b> within the receiver <b>10</b> while being articulatable or pivotal in unison with the upper portion <b>8</b> within the receiver <b>10</b>. The retainer <b>12</b>, best illustrated in FIGS. <b>1</b> and <b>3</b>-<b>5</b>, has an operational central axis that is the same as the rotational axis A associated with the shank <b>4</b>, but when the retainer structure <b>12</b> is separated from the shank <b>4</b>, the axis of rotation is identified as axis C, as shown in <figref idref="DRAWINGS">FIG. 1</figref>. The retainer structure <b>12</b> has a central bore, generally <b>95</b>, that passes entirely through the retainer structure <b>12</b> from a top surface <b>96</b> to a bottom surface <b>97</b> thereof. Both the top surface <b>96</b> and the bottom surface <b>97</b> are substantially planar and disposed perpendicular to the axis C. An inner discontinuous and substantially cylindrical surface <b>99</b> defines a substantial portion of the bore <b>95</b>. The cylindrical surface <b>99</b> is sized and shaped to be slidingly received and frictionally engaged about a lower section of the cylindrical surface portion <b>35</b> of the shank upper portion <b>8</b>. The cylindrical surface <b>99</b> has an axial length (along the axis C) that is relatively small compared to an overall axial length of the retainer structure <b>12</b>. Such relatively small axial length advantageously cooperates with the axial length of the cylindrical surface portion <b>35</b> of the shank upper portion <b>8</b> to provide sufficient space between the retainer structure <b>12</b> and the insert <b>14</b> during operation of the assembly <b>1</b>. In the illustrated embodiment, an inner discontinuous substantially conical surface <b>100</b> defines a substantial portion of the bore <b>95</b>. The conical surface <b>100</b> is sized and shaped to be slidingly received and frictionally engaged about the conical surface portion <b>33</b> of the shank upper portion <b>8</b>. A discontinuous and substantially planar annular seating surface <b>101</b> is disposed between and connects the surface <b>99</b> with the off-set surface <b>100</b>. The seating surface <b>101</b> is disposed substantially perpendicular to the axis C. The seating surface <b>101</b> is sized and shaped to abut against and frictionally engage the seating surface <b>34</b> of the shank upper portion <b>8</b>. The cooperating surfaces <b>99</b> and <b>35</b>; <b>100</b> and <b>33</b>; and <b>101</b> and <b>34</b> prohibit the retainer structure <b>12</b> from sliding off of the upper portion <b>8</b> in a direction toward the U-shaped channel <b>66</b>. The retainer structure <b>12</b> further includes a discontinuous curvate or spherical outer surface <b>103</b> and a discontinuous bevel <b>104</b> disposed between the outer surface <b>103</b> and the top surface <b>96</b>. A gap, generally <b>105</b> is defined by and disposed between facing side surfaces <b>106</b> and <b>107</b>. The gap <b>105</b> or space between the surfaces <b>106</b> and <b>107</b> in this embodiment is sized for slidingly receiving the rib <b>40</b> between the surfaces <b>106</b> and <b>107</b>. Surfaces <b>106</b> and <b>107</b> can be parallel or somewhat tapered and the fin can have matching side surfaces.

0047As will be described in greater detail below, the retainer structure <b>12</b> is somewhat flexible and resilient and may be manipulated or squeezed by moving the surfaces <b>106</b> and <b>107</b> toward one another as illustrated in <figref idref="DRAWINGS">FIG. 6</figref> or, if necessary, slightly pulled apart for receiving the fin or rib <b>40</b> during assembly with the shank <b>4</b> as illustrated in <figref idref="DRAWINGS">FIGS. 7 and 8</figref>. The resilient nature of the structure <b>12</b> allows for the structure <b>12</b> to spring into an original shape as shown in <figref idref="DRAWINGS">FIGS. 1</figref>, <b>3</b> and <b>7</b> upon release of a manipulative compressing or pulling force.

0048The retainer structure <b>12</b> outer surface <b>103</b> can also be knurled and is sized and shaped to mate with the seating surface <b>84</b> of the receiver <b>10</b> which in addition can be knurled. When in a non-compressed state, a width of the surface <b>103</b> is larger than the width of the neck <b>88</b> of the receiver <b>10</b>. The shank upper portion <b>8</b> conical surface <b>33</b>, annular seat <b>34</b> and cylindrical surface <b>35</b>, when engaged with the retainer <b>12</b>, fix the retainer <b>12</b> at a desired diameter or width such that the retainer <b>12</b> is prohibited from moving through the receiver neck <b>88</b> and out of the receiver <b>10</b>. Although not required, it is foreseen that the outer surface <b>103</b> may be a high friction surface such as a knurled surface, sand blasted surface, or the like. It is foreseen that in some embodiments of the invention, the retainer top surface <b>96</b> and the shank upper portion <b>8</b> may be configured so that the upper flat surface <b>96</b> abuts and supports a mating surface on the shank upper portion.

0049With reference to FIGS. <b>1</b> and <b>8</b>-<b>10</b>, the compression insert <b>14</b> is sized and shaped to be received by and downloaded or uploaded into the receiver <b>10</b>. In the illustrated embodiment, the insert <b>14</b> is downloaded into the receiver as shown in <figref idref="DRAWINGS">FIG. 8</figref>. In operation, the insert <b>14</b> is disposed between the rod <b>21</b> and the upper portion <b>8</b> of the bone screw <b>4</b> as illustrated, for example, in <figref idref="DRAWINGS">FIG. 10</figref>. When the closure structure <b>18</b> presses upon the rod <b>21</b>, the rod <b>21</b> operatively presses upon the insert <b>14</b> that in turn presses exclusively upon the shank upper end portion <b>8</b>, a portion of which is attached to the retainer <b>12</b>, that, in turn, presses against the seating surface <b>84</b> of the receiver <b>10</b>, resulting in ultimate frictional engagement and locking of the angular position of the bone screw shank <b>4</b> with respect to the receiver <b>10</b>. The compression insert <b>14</b> has an operational central axis D that is the same as the central axis B of the receiver <b>10</b>.

0050With particular reference to <figref idref="DRAWINGS">FIGS. 8-10</figref>, the compression insert <b>14</b> has a central channel or through bore substantially defined by a an inner cylindrical surface <b>110</b> and an inner partially spherical surface <b>112</b>, both having the central axis D. The compression insert <b>14</b> through bore is sized and shaped to receive a driving tool (not shown) therethrough that engages the shank drive feature <b>42</b> when the shank body <b>6</b> is driven into bone. The surface <b>112</b> is sized and shaped to cooperate with the spherical or otherwise curvate surface <b>36</b> of the shank upper portion <b>8</b> for polyaxial motion of the screw <b>1</b> such that the surface <b>112</b> slidingly and pivotally mates with the surface <b>36</b>. The surface <b>112</b> may include a roughening or surface finish to aid in frictional contact between the surface <b>112</b> and the surface <b>36</b>, once a desired angle of articulation of the shank <b>4</b> with respect to the receiver <b>10</b> is reached.

0051The compression insert <b>14</b> also includes a pair of arms <b>114</b> with a U-shaped surface or saddle <b>116</b> formed therebetween. The saddle <b>116</b> defines a U-shaped channel that communicates with the bore defined by the cylindrical surface <b>110</b> and the spherical surface <b>112</b>. The curved surface or saddle <b>116</b> is sized and shaped to closely receive the cylindrical rod <b>21</b>. With reference to the axis D, the saddle <b>116</b> extends from top surfaces <b>118</b> of the arms to a curved lower seat <b>120</b> near a bottom surface <b>122</b> of the insert <b>114</b>. In operation, the lower seat <b>120</b> (as well as a substantial portion of a remainder of the saddle <b>116</b>) frictionally engages the surface <b>22</b> of the rod <b>21</b>.

0052A base having an outer cylindrical surface <b>124</b> is disposed between the saddle <b>116</b> and the bottom surface <b>122</b>. The cylindrical surface <b>124</b> also extends about the arms <b>114</b>. Formed in the surface <b>124</b> and located centrally with respect to each arm <b>114</b> outer cylindrical surface is a shallow groove <b>126</b> having a substantially flat surface. The grooves <b>126</b> are sized and shaped to cooperate with the tabs <b>76</b> of the receiver <b>10</b> as will be described in greater detail below. Thus, although the grooves <b>126</b> may be of any shape, they are preferably elongate with the flat surface running parallel to the axis D and having a width that receives the respective tab <b>76</b>. The bottom surface <b>122</b> is substantially planar and annular and disposed perpendicular to the axis D.

0053The compression or pressure insert <b>14</b> ultimately seats exclusively on the shank upper portion <b>8</b> and is disposed substantially in the upper cylindrical portion <b>86</b> of the cavity <b>82</b>, with the tabs <b>76</b> engaging the insert <b>14</b> at the grooves <b>126</b>, thereby holding the insert <b>14</b> in desired alignment with respect to the rod <b>21</b> as will be described in greater detail below. In operation, the insert <b>14</b> extends at least partially into the channel <b>66</b> such that the saddle <b>116</b> surface substantially contacts and engages the outer surface <b>22</b> of the rod <b>21</b> when such rod is placed in the receiver <b>10</b> and the closure structure or top <b>18</b> is tightened therein.

0054With reference to <figref idref="DRAWINGS">FIGS. 1 and 10</figref>, the closure structure or closure top <b>18</b> can be any of a variety of different types of closure structures for use in conjunction with the present invention with suitable mating structure on the upstanding arms <b>62</b>. In the embodiment shown, the closure top <b>18</b> is rotatably received between the spaced arms <b>62</b>, but could be a turn-cam, slide-in or other type of closure structure. The illustrated closure structure <b>18</b> is substantially cylindrical and includes an outer helically wound guide and advancement structure <b>132</b> in the form of a flange form that operably joins with the guide and advancement structure <b>72</b> disposed on the arms <b>62</b> of the receiver <b>10</b>. The flange form utilized in accordance with the present invention may take a variety of forms, including those described in Applicant's U.S. Pat. No. 6,726,689, which is incorporated herein by reference. It is also foreseen that according to the invention the closure structure guide and advancement structure could alternatively be a buttress thread, a square thread, a reverse angle thread or other thread like or non-thread like helically wound advancement structure for operably guiding under rotation and advancing the closure structure <b>18</b> downward between the arms <b>62</b> and having such a nature as to resist splaying of the arms <b>62</b> when the closure structure <b>18</b> is advanced into the U-shaped channel <b>66</b>. The illustrated closure structure <b>18</b> also includes a top surface <b>134</b> with an internal drive <b>136</b> in the form of an aperture that may be a hex drive, or as illustrated, a star-shaped internal drive, for example, sold under the trademark TORX or other internal drives such as slotted, tri-wing, spanner, two or more apertures of various shapes, and the like. A driving tool (not shown) sized and shaped for engagement with the internal drive <b>136</b> is used for both rotatable engagement and, if needed, disengagement of the closure <b>18</b> from the receiver arms <b>62</b>. It is also foreseen that the closure structure <b>18</b> may alternatively include a break-off head designed to allow such a head to break from a base of the closure at a preselected torque, for example, 70 to 140 inch pounds. Such a closure structure would also include a base having an internal drive to be used for closure removal. A bottom surface <b>138</b> of the closure may be planar or include a point, points, a rim or roughening for engagement with the surface <b>22</b> of the rod <b>21</b>. The closure top <b>18</b> may further include a cannulation through bore extending along a central axis thereof and through the top surface <b>134</b> and the bottom surface <b>138</b>. Such a through bore provides a passage through the closure <b>18</b> interior for a length of wire (not shown) inserted therein to provide a guide for insertion of the closure top into the receiver arms <b>62</b>.

0055The elongate rod or longitudinal member <b>21</b> that is utilized with the assembly <b>1</b> can be any of a variety of implants utilized in reconstructive spinal surgery, but is normally a cylindrical elongate structure having the illustrated cylindrical surface <b>22</b> of uniform diameter and having a generally smooth surface. Although a cylindrical rod is shown, a variety of shapes are possible, including but not limited to bars of square or rectangular cross section, oval cross-section, and the like. Furthermore, the rod <b>21</b> may be a component of a dynamic stabilization connecting member, with the rod or rod portion <b>21</b> that is operatively disposed within the U-shaped channel <b>66</b> also being integral or otherwise fixed to a more flexible, bendable or damping component that extends between adjacent pairs of bone screw assemblies <b>1</b>. Such a rod or rod component may be made from a variety of materials including metal, metal alloys or other suitable materials, including, but not limited to plastic polymers such as polyetheretherketone (PEEK), ultra-high-molecular weight-polyethylene (UHMWP), polyurethanes and composites, including composites containing carbon fiber. Also, the connecting component can be a polyethylene-like cord that can be tensioned.

0056With particular reference to <figref idref="DRAWINGS">FIG. 5</figref>, prior to the polyaxial bone screw assembly <b>1</b> being placed in use according to the invention, the tip <b>28</b> of the shank <b>6</b> is inserted into the through bore <b>95</b> of the retainer structure <b>12</b> and the structure <b>12</b> is moved or threaded up the shaft <b>6</b> of the shank <b>4</b> to a position about the neck <b>26</b> near the shank upper portion <b>8</b>. The gap <b>105</b> between the surfaces <b>106</b> and <b>107</b> allows for such movement and the surfaces <b>106</b> and <b>107</b> may be pulled away from one another to provide clearance about the shank thread <b>24</b>, if necessary. Alternatively, in some embodiments, the surfaces <b>106</b> and <b>107</b> may be moved or pulled away from one another, widening the gap <b>105</b> and allowing the retainer <b>12</b> to be slipped over and around the shank <b>4</b> at the neck <b>26</b>. With reference to <figref idref="DRAWINGS">FIG. 6</figref>, the retainer structure <b>12</b> is then squeezed with the surfaces <b>106</b> and <b>107</b> being moved close together and a width and outer circumference of the retainer <b>12</b> being compressed to allow for bottom loading of the compressed retainer <b>12</b> and the shank upper portion <b>8</b> into the receiver <b>10</b> through the bore <b>90</b> defined by the neck <b>88</b>. As the shank upper portion <b>8</b> is inserted into the cavity <b>82</b> toward the U-shaped channel <b>66</b> and is slid along the cylindrical surface <b>86</b>, the spring tabs <b>76</b> are moved outwardly away from the axis A by the curved or radiused upper surface <b>36</b> of the shank upper portion <b>8</b>. The outer cylindrical surface portion <b>35</b> presses against the spring tabs <b>76</b>, keeping the tabs in an out-of-the-way position during assembly of the shank upper portion <b>8</b> with the retainer structure <b>12</b>.

0057With reference to <figref idref="DRAWINGS">FIG. 7</figref>, the retainer structure <b>12</b>, now disposed in the receiver <b>10</b> is released from compression, allowing the gap <b>105</b> to return to an original width shown in <figref idref="DRAWINGS">FIG. 1</figref>. The retainer structure <b>12</b> is then seated within the receiver <b>10</b> with the outer spherical surface <b>103</b> in sliding engagement with the receiver inner spherical seating surface <b>84</b>. The rib <b>40</b> of the shank upper portion <b>8</b> is then coaxially aligned with the gap <b>105</b> of the retainer structure <b>12</b> and the shank body <b>6</b> is pulled downwardly away from the U-shaped channel <b>66</b> so that the rib <b>40</b> is received into the gap <b>105</b> and slidingly moved along the axes A and C between the side surfaces <b>106</b> and <b>107</b> of the retainer structure <b>12</b> until the seating surface <b>101</b> abuts the seating surface <b>34</b>. At that time the conical surface portion <b>33</b> of the shank upper portion <b>8</b> is received within the inner conical surface <b>100</b> of the retainer <b>12</b> and a portion of the cylindrical surface portion <b>35</b> of the shank upper portion <b>8</b> is received within the inner cylindrical surface <b>99</b> of the retainer <b>12</b>. As illustrated in <figref idref="DRAWINGS">FIG. 8</figref>, when the seating surfaces <b>101</b> and <b>34</b> engage, the outer spherical surface <b>56</b> of the rib <b>40</b> is flush with the outer spherical surface <b>103</b> of the retainer structure <b>12</b> and the bevels <b>58</b> and <b>104</b> also are flush. Also as illustrated in <figref idref="DRAWINGS">FIG. 8</figref>, the rib <b>40</b> is sized and shaped such that the side surface <b>54</b> frictionally engages the side surface <b>106</b> of the retainer structure <b>12</b> and the side surface <b>55</b> frictionally engages the side surface <b>107</b> of the retainer structure <b>12</b>. As the shank upper portion <b>8</b> is pulled downwardly into the retainer <b>12</b> and into the cavity or chamber <b>82</b>, the spring tabs <b>76</b> return to a position with the lower ends <b>80</b> extending toward the axis B.

0058Preferably, the shank <b>4</b> and or the retainer <b>12</b> are aligned and engaged to a fully frictionally mated position at a factory setting that includes tooling for holding and precise alignment until locking frictional engagement therebetween is accomplished. Permanent, rigid engagement of the shank upper portion <b>8</b> to the retainer structure <b>12</b> may be further supported by the use of adhesive, a spot weld, a deformation, or the like. At this time the shank <b>4</b> and the attached retainer <b>12</b> are fixed or coupled to one another and both are in pivotal swivelable engagement with respect to the receiver <b>10</b>. The retainer <b>12</b> is in slidable engagement with the receiver curvate seating surface <b>84</b>. The shank body <b>6</b> can be rotated through a substantial angular rotation relative to the receiver <b>10</b>, both from side to side and from front to rear so as to substantially provide a universal or ball joint. The radiused or curved surface <b>36</b> of the shank upper portion <b>8</b> is also sized and shaped to clear a juncture between the cylindrical surface <b>86</b> and the spherical seating surface <b>84</b>, if a more extreme angular position is desired.

0059The compression or pressure insert <b>14</b> is then inserted or top loaded into the upper opening <b>67</b> of the U-shaped channel <b>66</b> of the receiver <b>10</b> with the bottom surface <b>122</b> facing the top surface <b>38</b> of the shank upper portion <b>8</b> and the arms <b>118</b> aligned with the arms <b>62</b> of the receiver <b>10</b> as illustrated in <figref idref="DRAWINGS">FIG. 8</figref>. As the insert <b>14</b> is moved downwardly toward the cylindrical portion <b>86</b>, the tabs <b>76</b> are received in respective grooves <b>126</b>. The tabs <b>76</b> press against the insert <b>14</b> at the grooves <b>126</b>, allowing for some upward and downward adjustment of the insert <b>14</b>. However, rotation of the insert <b>14</b> about the receiver axis B is prohibited by the tabs <b>76</b> abutting against cylindrical surfaces of the arms <b>114</b>. Surfaces defining the lower curved portion of the grooves <b>126</b> also prohibit the tabs <b>76</b> from sliding along the outer cylindrical surface of the base <b>124</b>, thus resisting upward movement of the insert <b>14</b> out of the receiver <b>10</b>. As illustrated in <figref idref="DRAWINGS">FIG. 10</figref>, the insert <b>14</b> seats on the shank upper portion <b>8</b> with the surface <b>112</b> in sliding engagement with the surface <b>36</b>. The shank body <b>6</b> can still be rotated through a substantial angular rotation relative to the receiver <b>10</b>, both from side to side and from front to rear so as to substantially provide a universal or ball joint, during which the insert <b>14</b> remains spaced from the retainer structure <b>12</b>.

0060In use, the assembly <b>1</b> is typically screwed into a bone, such as a vertebra (not shown), by rotation of the shank <b>4</b> using a driving tool (not shown) that operably drives and rotates the shank <b>4</b> by non-slip engagement thereof with the tool engagement structure <b>42</b>. The vertebra (not shown) may be pre-drilled to minimize stressing the bone and have a guide wire (not shown) that is shaped for the cannula <b>44</b> inserted to provide a guide for the placement and angle of the shank <b>4</b> with respect to the vertebra. A further tap hole may be made using a tap with the guide wire as a guide. Then, the assembly <b>1</b> is threaded onto the guide wire utilizing the cannulation bore <b>44</b> by first threading the wire into the bottom opening <b>46</b> and then out of the top at the internal drive <b>42</b>. The shank <b>4</b> is then driven into the vertebra, using the wire as a placement guide.

0061With reference to <figref idref="DRAWINGS">FIG. 10</figref>, the rod <b>21</b> is eventually positioned in an open or percutaneous manner within the receiver U-shaped channel <b>66</b>, and the closure structure or top <b>18</b> is then inserted into and advanced between the arms <b>62</b> so as to bias or push against the rod <b>21</b>. Alignment of the rod surface <b>22</b> with the saddle <b>116</b> of the insert <b>14</b> is initially provided and then maintained by pressure placed at the insert grooves <b>126</b> by the tabs <b>76</b>. The closure structure <b>18</b> is rotated, using a tool engaged with the inner drive <b>136</b> until a selected pressure is reached at which point the rod <b>21</b> engages the saddle <b>116</b> and the rod is urged toward, but not in contact with the lower seat <b>68</b> of the receiver <b>10</b> that defines the U-shaped channel <b>66</b>. For example, about 80 to about 120 inch pounds pressure may be required for fixing the bone screw shank <b>6</b> with respect to the receiver <b>10</b>.

0062As the closure structure <b>18</b> rotates and moves downwardly into the receiver <b>10</b>, the bottom surface <b>138</b> presses against the rod surface <b>22</b>, biasing the rod into engagement with the compression insert <b>14</b> that operably produces a frictional engagement between the insert surface <b>112</b> and the shank surface <b>36</b>, urging the shank upper portion <b>8</b> and attached retainer <b>12</b> in a direction toward the base <b>60</b> of the receiver <b>10</b>, so as to frictionally seat the spherical surface <b>103</b> of the retainer <b>12</b> against the inner spherical surface <b>84</b> of the receiver <b>10</b>, also fixing the shank <b>4</b> and the retainer <b>12</b> in a selected, rigid position relative to the receiver <b>10</b>. At this time it is also possible for the retainer <b>12</b> to expand somewhat for an even tighter fit in the receiver cavity lower seat <b>84</b>. This is especially so if the gap in the retainer is somewhat tapered or wedged in shape. However, the retainer <b>12</b> does not come into contact with the insert <b>14</b>, the insert <b>14</b> being exclusively seated on and pressing upon the shank upper portion <b>8</b> in any and all articulated positions of the shank <b>4</b> with respect to the receiver <b>10</b>. The retainer structure <b>12</b> that is spaced from the insert <b>14</b> engages only the shank upper portion <b>8</b> and the receiver <b>10</b>; the structure <b>12</b> being pressed upon by the upper portion <b>8</b> and in turn pressing upon the receiver <b>10</b> inner seating surface.

0063If removal of the rod <b>21</b> from any of the bone screw assemblies <b>1</b> is necessary, or if it is desired to release the rod <b>21</b> at a particular location, disassembly is accomplished by using the driving tool (not shown) that mates with the internal drive <b>136</b> on the closure structure <b>18</b> to rotate and remove the closure structure <b>18</b> from the cooperating receiver <b>10</b>. Disassembly is then accomplished in reverse order to the procedure described previously herein for assembly.

0064With reference to <figref idref="DRAWINGS">FIGS. 11-14</figref>, an alternative bone screw assembly of the invention, generally <b>201</b> includes a shank <b>204</b> that further includes a body <b>206</b> integral with an upper portion or capture structure <b>208</b>; a head or receiver <b>210</b>; a retainer <b>212</b> illustrated as an open retaining and articulating structure; and a compression insert <b>214</b>. With reference to <figref idref="DRAWINGS">FIGS. 11 and 14</figref>, the assembly <b>201</b> cooperates with a closure structure <b>218</b> and a rod <b>221</b>. The receiver <b>210</b>, the compression insert <b>214</b>, the closure structure <b>218</b> and the rod <b>221</b> are identical or substantially similar to the respective receiver <b>10</b>, insert <b>14</b>, closure structure <b>18</b> and rod <b>21</b> previously described herein with respect to the assembly <b>1</b>.

0065The shank <b>204</b> is substantially similar to the shank <b>4</b> previously described herein with the exception that the shank <b>204</b> does not include a rib or fin similar to the rib <b>40</b> of the shank upper portion <b>8</b> and the conical surface <b>33</b> is replaced by a cylindrical surface <b>233</b>. The shank <b>204</b> is elongate, with the shank body <b>206</b> having a helically wound bone implantable thread <b>224</b> extending from near a neck <b>226</b> located adjacent to the upper portion <b>208</b> to a tip <b>228</b> of the body <b>206</b> and extending radially outwardly therefrom. During use, the body <b>206</b> utilizing the thread <b>224</b> for gripping and advancement is implanted into the vertebra (not shown) leading with the tip <b>228</b> and driven down into the vertebra with an installation or driving tool, so as to be implanted in the vertebra to near the neck <b>226</b>, and as is described more fully in the paragraphs below. The shank <b>204</b> has an elongate axis of rotation generally identified by the reference letter E.

0066The neck <b>226</b> extends axially upwardly from the shank body <b>206</b>. The neck <b>226</b> may be of reduced radius as compared to an adjacent top <b>232</b> of the threaded body <b>206</b>. Further extending axially upwardly from the neck <b>226</b> is the shank upper portion <b>208</b> that provides a connective or capture apparatus disposed at a distance from the threaded body top <b>232</b> and thus at a distance from the vertebra when the body <b>206</b> is implanted in the vertebra. To provide a biologically active interface with the bone, the threaded shank body <b>206</b> may be coated, perforated, made porous or otherwise treated as previously described herein with respect to the shank body <b>6</b>.

0067The shank upper portion <b>208</b> is configured for a polyaxial connection between the shank <b>204</b> and the receiver <b>210</b> and capturing the shank <b>204</b> upper portion <b>208</b> in the receiver <b>210</b>. The upper portion <b>208</b> generally includes the first, lower or in-set cylindrical surface portion <b>233</b> located adjacent the neck <b>226</b>; an annular planar retainer seat portion <b>234</b>; an off- or out-set substantially cylindrical second surface portion <b>235</b>; a curved and annular upper surface <b>236</b> and a planar top surface <b>238</b>. The planar top surface <b>238</b> is substantially perpendicular to the cylindrical surface portion <b>235</b> and substantially parallel to the seat portion <b>234</b>. The cylindrical portion <b>233</b> extends between the neck <b>26</b> and the retainer seat <b>34</b>. The retainer seat <b>234</b> defines a lower edge <b>239</b> of the cylindrical portion <b>235</b>. A tool engagement internal drive feature or structure <b>242</b> is formed in the top end surface <b>238</b>. A driving tool (not shown) has a driving projection configured to fit within the tool engagement structure <b>242</b> for both driving and rotating the shank body <b>206</b> into the vertebra.

0068The upper surface <b>236</b> of the shank <b>204</b> is preferably curved or radiused as shown in the drawings, for exclusive contact engagement or positive mating engagement with the compression insert <b>214</b>, when the bone screw assembly <b>201</b> is assembled, as shown in <figref idref="DRAWINGS">FIG. 14</figref> and in any alignment of the shank <b>204</b> relative to the receiver <b>210</b>. The illustrated surface <b>236</b> also has approximately the same radius as an inner spherical seating surface of the receiver <b>210</b>, allowing for clearance of the shank <b>204</b> with respect to the receiver <b>210</b> and thus a desired degree and magnitude of articulation of the shank <b>204</b> with respect to the receiver <b>210</b>. In certain embodiments, the surface <b>236</b> is smooth. While not required in accordance with the practice of the invention, the surface <b>236</b> may be scored or knurled to further increase frictional positive mating engagement between the surface <b>236</b> and the compression insert <b>214</b>.

0069The shank <b>204</b> shown in the drawings is cannulated, having a small central bore <b>244</b> extending an entire length of the shank <b>204</b> along the axis E. The bore <b>244</b> is defined by an inner cylindrical wall of the shank <b>204</b> and has a circular opening <b>246</b> at the shank tip <b>228</b> and an upper opening communicating with the internal drive <b>242</b>. The bore <b>244</b> is coaxial with the threaded body <b>206</b> and the upper portion <b>208</b>. The bore <b>244</b> provides a passage through the shank <b>204</b> interior for a length of wire (not shown) inserted into the vertebra (not shown) prior to the insertion of the shank body <b>206</b>, the wire providing a guide for insertion of the shank body <b>206</b> into the vertebra (not shown). The retainer seat <b>234</b> of the shank upper portion <b>208</b> is a substantially planar annular surface disposed perpendicular to the Axis E of the shank and sized and shaped to engage the retainer structure <b>212</b> as will be described in greater detail below. The first or inner cylindrical surface portion <b>233</b> and the second or outer cylindrical surface portion <b>235</b> are also sized and shaped to slidingly engage portions of the retainer structure <b>212</b>, also described in greater detail subsequently herein.

0070The retainer structure or open ring <b>212</b> is used to capture the shank upper portion <b>208</b> and retain the upper portion <b>208</b> within the receiver <b>210</b>. The retainer <b>212</b>, best illustrated in <figref idref="DRAWINGS">FIGS. 12 and 13</figref>, has an operational central axis that is the same as the rotational axis E associated with the shank <b>204</b>, but when the retainer structure <b>212</b> is separated from the shank <b>204</b>, the axis of rotation is identified as axis G. The retainer structure <b>212</b> has a central bore, generally <b>285</b>, that passes entirely through the retainer structure <b>212</b> from a top surface <b>286</b> to a bottom surface <b>287</b> thereof. Both the top surface <b>286</b> and the bottom surface <b>287</b> are substantially planar and disposed perpendicular to the axis G. An inner discontinuous and substantially cylindrical surface <b>289</b> defines a substantial portion of the bore <b>285</b>. The cylindrical surface <b>289</b> is sized and shaped to be slidingly received and frictionally engaged about a lower segment of the cylindrical surface portion <b>235</b> of the shank upper portion <b>208</b>. An inner discontinuous substantially cylindrical surface <b>290</b> also defines a substantial portion of the bore <b>285</b>. The cylindrical surface <b>290</b> is sized and shaped to be slidingly received and frictionally engaged about the in-set or inner cylindrical surface portion <b>233</b> of the shank upper portion <b>208</b>. A discontinuous and substantially planar annular seating surface <b>291</b> is disposed between and connects the surface <b>289</b> with the surface <b>290</b>. The seating surface <b>291</b> is disposed substantially perpendicular to the axis G. The seating surface <b>291</b> is sized and shaped to abut against and frictionally engage the seating surface <b>234</b> of the shank upper portion <b>208</b>. The cooperating cylindrical surfaces <b>289</b> and <b>235</b>; cylindrical surfaces <b>290</b> and <b>233</b>; and planar annular abutting seating surfaces <b>291</b> and <b>234</b> cooperate to prohibit the retainer structure <b>212</b> from sliding in a direction upwardly off of the upper portion <b>208</b> toward a U-shaped channel of the receiver <b>210</b>. It is foreseen a shank upper portion and retainer structure combination according to the invention may alternatively include cooperating conical surfaces or a conical surface cooperating with a cylindrical surface and cooperating abutting or seat surfaces adjacent to planar or other shaped surfaces in lieu of or in addition to the illustrated cooperating cylindrical surfaces. It is also foreseen that shank upper portion and retainer structure combinations according to the invention may include cooperating conical or cylindrical surfaces and not include the illustrated abutting annular surfaces <b>234</b> and <b>291</b>.

0071The retainer structure <b>212</b> further includes a discontinuous curvate outer surface <b>293</b> and a discontinuous bevel <b>294</b> disposed between the outer surface <b>293</b> and the top surface <b>286</b>.

0072A gap or slit, generally <b>295</b> is defined by and disposed between facing side surfaces <b>296</b> and <b>297</b>. The side surface <b>296</b> and <b>297</b>, in the embodiment shown, are substantially parallel and evenly spaced from one another and are disposed at an oblique angle with respect to the top surface <b>286</b> and the bottom surface <b>287</b>, but other configurations are possible. The gap or slit <b>295</b> allows for the somewhat flexible and resilient retainer structure <b>212</b> to be squeezed, compressed, expanded, or otherwise manipulated by moving the surfaces <b>296</b> and <b>297</b> toward or away from one another and in opposite directions with reference to the axis G. The resilient nature of the structure <b>212</b> allows for the structure <b>212</b> to spring back into an original shape as shown in <figref idref="DRAWINGS">FIGS. 11 and 14</figref> after being manipulated. As will be described in greater detail below, the oblique orientation of the surfaces <b>296</b> and <b>297</b> allows for a desired narrow gap or slit <b>295</b> to be sufficient for bottom loading of the structure <b>212</b> as the surfaces <b>296</b> and <b>297</b> slide against each other when the structure <b>212</b> is squeezed, for example, the surface <b>296</b> moving upwardly and the surface <b>297</b> moving downwardly or oppositely with respect to the axis G. Thus, such oblique orientation of the surfaces <b>296</b> and <b>297</b> provides for sufficient minimizing of a width or circumference of the structure <b>212</b> for bottom loading into the receiver <b>210</b> and also provides almost full coverage of the structure <b>212</b> about the shank upper portion <b>208</b> when the structure <b>212</b> is engaged with the portion <b>208</b> and operatively disposed within the receiver <b>210</b>. Again, it is foreseen that in other embodiments according to the invention, the surfaces <b>296</b> and <b>297</b> may be disposed at other oblique angles or alternatively substantially perpendicular to the top and bottom surfaces <b>286</b> and <b>287</b>. In such an alternative embodiment, a gap between the surfaces <b>296</b> and <b>297</b> may be wider than the illustrated gap <b>285</b>.

0073The retainer structure <b>212</b> radially outer substantially spherically shaped surface <b>293</b> is sized and shaped to mate with the spherically shaped inner seating surface of the receiver <b>210</b> that is identical or substantially similar to the inner receiving surface <b>84</b> of the receiver <b>10</b> previously described herein with respect to the assembly <b>1</b>. When in a non-compressed state, a radius of the surface <b>293</b> is larger than the radius of a lower neck <b>288</b> of the receiver <b>210</b>. The shank upper portion <b>208</b> cylindrical surface <b>233</b>, annular seat <b>234</b> and cylindrical surface <b>235</b>, when engaged with the retainer <b>212</b>, fix the retainer <b>212</b> at a desired diameter or width such that the retainer <b>212</b> is prohibited from moving downwardly through the lower neck <b>288</b> and out of the receiver <b>210</b>. Although not required, it is foreseen that the outer curvate shaped surface <b>293</b> may be a high friction surface such as a knurled surface or the like.

0074With particular reference to <figref idref="DRAWINGS">FIG. 11</figref>, prior to the polyaxial bone screw assembly <b>201</b> being placed in use according to the invention, the tip <b>228</b> of the shank <b>206</b> is inserted into the through bore <b>285</b> of the retainer structure <b>212</b> and the structure <b>212</b> is moved or threaded up the shaft <b>206</b> of the shank <b>204</b> to a position about the neck <b>226</b> near the shank upper portion <b>208</b>. The gap <b>295</b> between the surfaces <b>296</b> and <b>297</b> allows for such movement and the surfaces <b>296</b> and <b>297</b> may be pulled away from one another to provide clearance about the shank thread <b>224</b>, if necessary. Alternatively, in some embodiments, the surfaces <b>296</b> and <b>297</b> may be moved or pulled away from one another, widening the gap <b>295</b> and allowing the retainer <b>212</b> to be slipped over and around the shank <b>204</b> at the neck <b>226</b>. The retainer structure <b>212</b> is then squeezed with the surfaces <b>296</b> and <b>297</b> moved into engagement with one another and the structure being slightly twisted to slide the surfaces <b>296</b> and <b>297</b> in opposite directions with respect to the axis G and thus the top surface <b>286</b> and the bottom surface <b>287</b> slightly contorted into a non-planar orientation to result in a width or outer circumference of the structure <b>212</b> small enough to enter the receiver <b>210</b> through the lower restrictive neck <b>288</b>. Such contorted and squeezed orientation of the structure <b>212</b> about the shank neck <b>226</b> allows for bottom loading of the compressed retainer <b>212</b> and the shank upper portion <b>208</b> into the receiver <b>210</b> through a bore defined by the neck <b>288</b>. The retainer structure <b>212</b>, now disposed in the receiver <b>210</b> is released from compression, allowing the slit or gap <b>295</b> to return to an original width and orientation shown in <figref idref="DRAWINGS">FIGS. 11 and 14</figref>. The retainer structure <b>212</b> is then seated within the receiver <b>210</b> with the outer spherical surface <b>293</b> in sliding engagement with an inner spherical seating surface of the receiver <b>210</b>. The shank body <b>206</b> is pulled downwardly toward the lower neck <b>288</b> and along the axes E and G until the seating surface <b>291</b> abuts the seating surface <b>234</b>. At that time the cylindrical surface portion <b>233</b> of the shank upper portion <b>208</b> is received within the inner cylindrical surface <b>290</b> of the retainer <b>212</b> and a portion of the cylindrical surface portion <b>235</b> of the shank upper portion <b>208</b> is received within the inner cylindrical surface <b>289</b> of the retainer <b>212</b>. Permanent, rigid engagement of the capture structure <b>208</b> to the retainer structure <b>212</b> may be further supported by the use of adhesive, a spot weld, a deformation, or the like. At this time the shank <b>204</b> and the attached retainer <b>212</b> are fixed to one another and both are in swivelable engagement with respect to the receiver <b>210</b>. The shank body <b>206</b> can be rotated or swivelled through a substantial angular rotation relative to the receiver <b>210</b>, both from side to side and from front to rear so as to substantially provide a universal or ball joint.

0075The compression or pressure insert <b>214</b> is then inserted or top loaded into the receiver <b>210</b> in a manner identical or similar to that described previously herein with respect to the insert <b>14</b> and the receiver <b>10</b>. As with the insert <b>14</b>, the insert <b>214</b> remains spaced from the retainer structure <b>212</b> as the shank body <b>206</b> is swivelled through a substantial angular rotation relative to the receiver <b>210</b>, both from side to side and from front to rear. With reference to <figref idref="DRAWINGS">FIG. 14</figref>, in use, the assembly <b>201</b> is typically implanted with a cooperating longitudinal connecting member, such as the rod <b>221</b>, as previously described herein with respect to the assembly <b>1</b>. The assembly <b>201</b> may also be disassembled as previously described herein with respect to the assembly <b>1</b>.

0076It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.